The need for an alternative and independent positioning system to GPS remains undiminished due to the vulnerability of GPS to external signal spoofing and other forms of signal disruption and denial (Pappalardi, et al., (2001). Alternatives to GPS. In OCEANS, 2001. MTS/IEEE Conference and Exhibition (Vol. 3, pp. 1452-1459). IEEE). To this end, the U.S. Navy continues to teach and practice celestial navigation. Conventional celestial navigation instruments, such as sextants, quadrants and the like, are typically mechanical-optical devices used to measure angles also called angular distances. The angular distance between two-point objects, as observed from a location different from either of these objects, is the size of the angle between the two directions originating from the observer and pointing towards these two objects. Altitude is the term of art for the angular distance of a celestial body above the observer's horizon. The term of art for the uncorrected measured angle between a celestial body, such as a star, a planet, sun, or moon and the horizon is called the “Sextant Altitude” of the body. It is difficult to accurately capture useful angular measurements like sextant altitudes with these devices because of several factors. 1) On a traditional sextant, the angle must be measured by physically altering the geometry of the device with sufficient precision, which is typically about 0.0033 degrees of arc. This usually involves multiple controls of increasing fine adjustment. 2) The measurement is often taken on a vehicle, such as a watercraft, aircraft, or the like, that is usually in motion including translation, roll, pitch, yaw and spin, making accurate manipulation of the device challenging. Taking such a measurement is so challenging, that extensive training and experience is typically required to successfully use such devices to practical effect, and still wide variation exists in the ability of practitioners. 3) The angle must be visually read off the device usually from a combination of increasingly fine scales of measurement. The combined value must then be recorded with the time of the measurement to within a second of accuracy. This will be repeated for every object measured, for a minimum of 2 but often 4 or more, to be used in determining the navigational location or “fix” as the term of art is known in the field. The recorded angles and times must then be submitted to corrections and calculations. Conditions like weather may reveal the objects for too brief a time for the sextant user to manipulate the device and capture the required angle or angles. Further, such devices require human operation, thus preventing practical autonomous celestial navigation.
While GPS is readily available it is known to be unreliable particularly in times and regions of conflict where combatants disrupt, alter, or provide false GPS signals. As such, celestial navigation is still widely practiced in spite of its challenges. Therefore, the need exists for a novel means to accurately measure angles without fine human manipulation of a sextant or similar device, and a device that is not dependent on external communications or venerable to disruption of spoofing from external singles.